sweetman



Feb. 14, 1956 w. G. swEETMAN GUN PERFORATOR 2 Sheets-Sheet l Filed April 2l, 1949 INVENTUR. n

ATTORNEY Feb. 14, 1956 W. G. SWEETMAN '2,734,456

GUN PERFORATOR 2 Sheets-Sheet 2 Filed April 2l 1949 inl 'III Il! 3 M .iid o@ A V d W ff.

INVENTOR. imam W. G, .ufee

ATTORNEY GUN PERFQRATR William G. Sweetman, Houston, Tex. ApplicationApril 21, 1949, Serial No. 83,740

4 Claims. (Cl. IGZ-21.6)

This invention relates to perforating devices, commonly called guns, which are employed to perforate the walls of wells, such as oil or gas wells, to provide communication between the well bore andthe fluids in the surrounding formations. More particularly, this invention is directed to perforating devices of the type which employ hollowed explosive charges rather than the more conventional bullet-type projectiles as the perforating elements.

The cavity or hollow charge principle, widely employed in World War Il in connection with explosives, has more recently been applied to the perforation of metal well casings and other well bore linings because of the superior penetrating power obtainable with such charges. For well perforating purposes, such charges are usually constructed in the form of small relatively high density bodies of high-brisance types of detonating explosives, having an end thereof facing the object to be pierced provided with a cavity or hollow, generally of conical Shape, which is lined with a thin metal liner. When suitably detonated, the major proportion of the generated explosive force is concentrated, by virtue of the shape of the hollow and liner, into a relatively narrow gaseous jet of tremendous power and penetrating force which is directed largely along the longitudinal axis of the hollow. Such perforating charges do not employ projectiles but depend substantially entirely upon the penetrating power of the gaseous jet to eect the desired degree of perforation.

Although, as noted, the major proportion of the force of such hollowed charges will be concentrated in a relatively narrow jet along the longitudinal axis of the cavity, nevertheless, very substantial radial forces and pressures will be generated at the same time which have proven ditlicult to control and confine in a manner which will prevent serious damage to the supporting gun bodies. The prevention of such damage to the gun bodies is important from the standpoint of maintaining the ring eihciency in repeated re-use and from an economic standpoint.

Perforating guns are operated in wells which are ordinarily filled with hydraulic fluids, such as heavy muds and the like, and the guns will, therefore, be subjected to hydrostatic pressures ranging to several thousand pounds per square inch in deep wells. This necessarily requires very careful machining of the gun bodies and particularly of the receptacles and seats for the perforating charges and the closures therefor, in order to assure Huid-tightness under such high pressures, since seepage of fluid into the charge receptacles and the interior passages in the gun body will cause mis-hres and other undesirable damage thereto.V Such gun bodies are, therefore, relatively expensive to construct and their repeated re-use is necessarily dictated for reasons of economy.

Accordingly, it is a primary object of this invention to provide an improved perforating gun employing hollowed-type perforating charges.

An important object isto` provide a gun which is United, States Patent 2,734,456 Patented Feb. A14, 1956 adapted for the repeated re-loading and firing of hollowed-type perforating charges.

Another important object is to provide such a gun in which a particular arrangement of the charges relative to their receptacles in the gun body is employed to protect the gun body from damage by the explosion of the charges.

Another object is the provision of an improved form of explosive perforating unit of the hollow-charge type.

Other and more specific objects and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings which illustrate useful embodiments in accordance with this invention.

In the drawings:

Fig. l is an elevational view of a gun in accordance with an embodiment of this invention assembled preparatory to lowering in a well and having some of the parts thereof broken away for purposes of better illustration;

Fig. 2 is an enlarged view in longitudinal section of a portion of the gun showing one of the perforating units in place therein;

Fig. 3 is a cross-sectional view along line 3 3 of Fig. 2;

Fig. 4 is an elevational view of a portion of the gun looking directly at the end of one of the perforating units;

Fig. 5 is a separated view of a perforating unit and closure therefor; and

Fig. 6 is an enlarged view, partly in section, showing the means for connecting two gun units together.

The gun perforator, in accordance with one embodiment of this invention, comprises a gun body 10 in the form of an elongated steel cylinder, preferably constructed from a solid billet, having a plurality of radially directed receptacles, indicated generally by the numerals 11, in which are seated perforating units, designated generally by the numerals 12, and closure elements, indicated generally by the numerals 13. Body 10 is preferably made from a solid steel billet,fheat treated and otherwise constructed -in the manner commonly used for the construction of the more conventional bullet-type perforating guns.

An internally threaded connection box 14 is provided at one end of body 10 and an externally threaded pin 15 at the other end thereof. A narrow passageway 16 extends axially through body 10 from the bottom of box 14 to the extremity of pin 15.

Receptacles 11, in the illustrative embodiment, are axially spaced and spirally oriented along the gun body but may all face in one direction or alternately in opposite directions, as may be desired.

Each of receptacles 11 includes a socket 17, of generally cylindrical form, which intersects passageway 16, and an outer mouth section 18 opening to one side of body 10. Outer section 18 is of substantially larger diameter than socket 17, thereby forming an annular shoulder 19 of substantial width about the outer end of socket 17. The peripheral wall 20 of outer section 18 diverges outwardly from shoulder 19 to its intersection with the outer periphery of body 10, thereby defining a frusto conical shape for outer section 18. Socket 17 has an inner end wall 21 which may be of generally plane form as illustrated, or may be generally spherical, parabolic or conical, or may be raised or embossed, if desired. The bore of passageway 16, at the points of its intersection with each of the sockets 17 may be laterally flared at one side, as at 22, to merge more or less smoothly into end wall 21.

Each of the perforating units 12 comprises an explosive'material 23 which may be molded, compressed or otherwise formed by conventional methods to provide a Vbody having an overall generally conical shape but which may havena cylindrically shaped base portionT 24'and' a generally cylindricalapex portion25. Base portion24 is provided with an axially outwardly directed cavity or hollow 26, which is preferably of a generally conical shape, but may behemispherical,parabolic orV ofy other suitable shape, and is lined -withfa `correspondingly shaped liner 27, preferablyV constructed -ofa suitable ythin* metal such ascopper, aluminum, steel or the like which2 is deformable and even rupturable.

Explosive material'23- is preferably one-of the well known high-brisance types of chemical detonatingrexplosives, which include suchv materials `are'pentaerythritol tetranitrate (.PETN), trinit-r'otoluene'- (TNT), Pentolite (50%- PETN -and"50% TNT); TetryL "Amatol, Cyclonite, Tetrytol (60% l Tetrfyl and40% TNT), and many others wellknown'in theexplosiveart. v Apex portion 2S may be in theform of-`af booster charge-composed of explosive materialof' thelsame general character as that composing the main body of explosive'21,l or may be adifferent'indvidualone, ormay bethe' very samel explosive material but of different density,` forexample, to supply the desired boostingy effect vupon the' main body of the explosive, such combinations and variations being well understood' inthe explosive art.

All ofthe explosive material is preferbaly encased within a relatively thin-walled container' 28,` thev inner wallsof which'closely correspond in shape to the external configurations of the body of explosive material. The exterior wall of container'28 may be generally conical, as shown, although other external shapes may be used. Container 28- maybe constructed of any suitable material, which may most conveniently: beone of the numerous synthetic plastics, which possesses sufficient rigidity and mechanical strength to support and hold the enclosed explosive inY the desired shape and to permit effective handling of theexplosiveY chargev as a unit, as in shipping and in loading into the gun body. The apex end of container 28 is providedwith-a transverse notch 29, perferably having a transversely roundedbottom wall 30 (Fig. 3), which extends axially somewhat into the interior of the container, the booster explosive comprising apex portion 2S," being correspondingly shaped to pack closely about the innerrcurved'surface of the bottom wall of the-notch, andto thereby extend upwardly on each side'of the bottom 'ofthehotch' to approximately cular and substantiallyiush with' the end'face of the' basev portion 24 `of the explosive and is adaptedto form an annular seat for the p eriphery' 'of liner' 27"when the latter is properly position'ed'in hollow 26'.` The maximum diameter ofthe explosive body, being the diameter of base portion 24, is made substantially'smaller than that of the bore of socket17 to provide a substantial clearance space therebetween for purposes to be described hereinafter. Th'e external diameter of container 28, while necessarily somewhat greater than that of base portion 24due to its wall thickness, is also made somewhat less than that of the bore of' socket 17 lso as to provide lan annular clearance space Vbetween theexterior of container 28andsocket 17.V

Each of the closure elements'13 comprises a tubular sleeve 31 formed with a closed louter end 'wall32, preferablyspherical or dome shaped, as shown, andis adapted to have its open inner end slidi'ngly inserted into socket 17'through the clearance space provided, as above described, between container 28 and the bore of the socket. The bore 33'of sleeve 31 is adapted to receive the base end of container 2,8 and is dimensioned to forml aclose slidingV fit therewith. An internal lshoulder 34 is provided' in'bore"33 axially' spaced 'from' end wall 32'to providea. spacing stop.. for positioning the hollowed end` of the perforating unit at somesuitable predetermined axial distance from end wall 32. The distance between the base of the explosive and the end wall forms the so-called stand-off distance. Closure element 32 is adapted to seal the stand-off space to exclude therefrom any extraneous material, such as mud, well fluid and the like, which might interfere with the development of an effective perforating jet. An outwardly extending annular ange 35 is provided about the exterior of sleeve 31, being preferably formed integral therewith, and is adapted to seat against shoulder 19. The external diameter of flange 35 is made somewhat less than that of shoulder 19 so that some degree of annular clearance is provided between the periphery of flange 35 and wall 20. A pair of cap screws 36-36 are adapted to be screwed into body 10 on diametrically opposite sides of flange 35 and are so positioned adjacent-thereto that-their heads will overlap the edge of flange 35. With this arrangement cap screws 36, whenscrewed into suitable threaded yholes in body 10, may be employed to clamp closure element 13 against shoulder 19 vand thereby to the gun body. A circular packing ring 37y is seated in the inner'face of flange 3S and is adapted, when the closure' elementis clamped against body 10 by means of cap screw'36, as described, to form a fluid-tight seal between shoulder 19- andthe inner'face of flange 35 thereby also forming a fluid-tight seal between the closure element and socket 17. Wall 20 is'provided with suitable recesses 38--38 to receive the cap screws so that they may be screwed down inside the periphery of thegunbody. Closure ele'- ment 31 may be'constructed of any suitable metal which, generally speaking, is softer than the steel of which body 16 is constructed butwhich has sufiicient strength to withstand hydrostatic pressures of the magnitudes which may be encountered in wells in which the gun is operated. Various aluminum and zinc alloys, copper, steel and the like may be used. A cast metal which is adapted to be fully shattered by the explosiorrof the perforating unit will be preferable in most cases. Flange 35 is positioned along the exterior of sleeve 31 inwardly relative to shoulder 34, so that when the'closure element is in place, shoulder 34 will always be radially spaced outwardly relative to the outer end of vsocket 17 as defined by shoulder 19. Thus when the perforating unit is inserted inthe clo# sure element with its base portion lodged against shoulder 34,"the base portion of the explosive charge will be positioned exteriorly ofthe'outer end 'of socket 17 and'within the enlarged mouth section 18.'

A suitable and generally conventional fuse element, which may be a length'or flexible detonating cord 39, such as the well known Prima Cord, is threaded through passageway 16"aud has the portions thereof pass-v ing through sockets 17 'seated in notches 29 in detonatingrelation to the inner ends of the explosive charges.'

A firing head'40, having a threaded pin 40a, is adapted to be screwed into box 14, to form a fluid-tight closure therefor, and has an axial passage 41 registering with passageway 16 through which the upper end of fuse cord 39 may be threaded.` The upper portion of passage 41 is enlarged somewhat in diameter to form a shoulder 42. The upper end of the fuse cord maybe knotted, as at 43, so thatit will lodge against shoulder 42, to prevent its being pulled downwardly out of the firing head. A conventional electrically-fired explosive initiator 44 is inserted in the enlarged portion of passage 41 in contact with the knottedend 43 of the fuse cord and is connected to a suitable electrical conductor 45, which extends to the upper end of the firing head and makes connection in the usual manner by means of a conventional cable connector 46, whichis adapted to beseparably connected to the firing head, to an electric cable.47 which is also employed for lowering the. gun into a well. It will be understood that cable 47 is adapted'to extend tothe 1 n ground surface where it may be connected to a conventional tiring mechanism, and an appropriate source of electric current (not shown). The lower end of fuse cord 39 may also be knotted, as at 48, as it emerges from the end of pin to hold the fuse cord in place in the gun body, and a metal cap 49 is screwed on pin 15 to form a lluid-tight closure for the lower end of the gun body.

The gun may be assembled and loaded in the following manner preparatory to lowering in a well: A piece of fuse cord 39 of suitable length is inserted through passage 41 of the firing head and knotted at its upper end at 43 to retain it in the head. `The free end of the cord is then threaded through passageway 16 and tiring head 40 is screwed down tightly into box 14, the lower end of cord 39 being extended through the end of pin 15 and knotted at 48 to prevent its retraction through passageway 16.

The perforating units 11 are preferably formed into subassemblies with closure elements 13, as illustrated by the exploded View shown in Fig. 5. A container 28 having the explosive material enclosed therein and a liner 27 in place in hollow 26 will be inserted into the open end of sleeve 31 and pushed home against shoulder 34. A coating of adhesive may be applied to the engaged surfaces of container 28 and bore 33 of the sleeve to hold the perforating unit in place and to exclude moisture from the stand-off space during further handling. The subassembly thus formed may then be inserted into one of the sockets 17, being oriented so that notch 29 will register longitudinally with the portion of the fuse cord 39 which traverses the socket. As the sub-assembly is pushed into the socket, the fuse cord will be engaged in notch 29 of the perforating unit and will be forced radially toward the rear wall 21 of the socket when the unit is fully inserted. The fuse cord will thus be placed under tension, and the normal reaction of the laterally displaced portions under this tension will serve to maintain the displaced portions of the fuse cord in tight engagement with the curved bottom 30 of notch 29, and to hold the perforating unit in firm engagement with shoulder 34. It will be understood that the lengthl of the fuse cord inserted in the gun body will have been predetermined to accommodate the several perforating units which are thus connected to the fuse cord in the gun body. As each sub-assembly is inserted in its socket, cap screws 36 will be put in place and screwed down to clamp the assembly tightly in place. Enlargements 22 at the intersections of passageway 16 with socket 17 provide smoothly tapering surfaces to accommodate the lateral displacement of the fuse cord by the thrust of the perforating units to thereby avoid the formation of sharp angular bends in the fuse cord, which would adversely affect the fusing action of the cord in transmitting the detonating wave to the successive charges connected thereto. By providing the transverse inward curvature of bottom wall 30 of notch 29, in the manner previously described, the portion of the detonating cord seated in the notch will thereby be at least partially surrounded by explosive material, so that upon detonation of the cord, the detonating wave will be transmitted radially into the main explosive charge over a relatively wide spread portion of the charge, thereby more eifectively applying the detonating force to the charge. Moreover, by curving the bottom wall of the notch outwardly longitudinally of the notch, in the manner previously described and as illustrated particularly in Figs. 2 and 5, a greater eective length of the detonating cord is placed in contact with the booster portion of the charge, thereby additionally increasing the eiectiveness of detonation and assuring high order detonation of the explosive charge.

When the gun has been loaded, as described above, cap 49 will be put in place to close the lower endof the gun body, initiator 44 will be inserted in passage 41 into skimmed a pressure contact with the 39, cable connector 46 will be connected to the upper end of ring head 40 and the gun will be ready for lowering into a well.

When a gun constructed and assembled as above described is fired, fuse cord 39 will first be detonated by the explosion of initiator 44 and will, in turn, detonate the several perforating charges in contact therewith. The detonation of the perforating charges will generate a gaseous jet of extremely high velocity and high pressure which will be directed outwardly along the longitudinal axis of the charge, shattering or disintegrating liner 27 and closure element 13 and, upon striking the well wall, will produce the desired penetration.

Upon detonation of the hollowed charge the resulting gases are directed generally along an axis. However, in accordance with the illustrative embodiments of this invention, there is interposed along such axis and in the path of the gases means which is rupturable by the gases, which is inthe form of liner 26, the gases will be converged to a relatively narrow column. This liner which acts as a converger, has such an angle and is made of such a material and thickness of material that it Will rupture upon detonation of the charge in a manner so as to deform the converger in the direction of the issuing gases in order Vto converge those gases to a relatively narrow column.

The `construction is, therefore, such as to not only cause the converging means to converge the resulting gases into l a relatively narrow column, but to actually cause penetration of the gases through the converger, so that the resulting jet will pass beyond the converging means rather than have the latter precede it, as in the case of the propelling oi a projectile. Moreover, the gases will be maintained in the form of a narrow column for an extendeddistance after convergence.

Although the major proportion of the energy of the explosive will be concentrated in the relatively narrow axially directed jet, very substantial radial forces will be simultaneously generated. By providing an annular air space, as described above, between the exterior of the body of the explosive material comprising the perforating charge and the wall of socket 17 and by positioning the base portion of the charge exteriorly of the end of the socket, in a manner substantially as illustrated in Figs. 2 and 3 particularly, the radial forces emanating from the sides and base portion will dissipate without serious deleterious action on the surrounding portions of the gun body. This desirable result is heightened by making the exterior of the explosive body conical in shape, as illustrated, whereby the exterior surfaces converge inwardly of the socket Land away from the socket wall thus enlarging the free air space between the explosive and the socket wall. Moreover, in a hollow explosive, fused to detonate from the end opposite the hollow toward the latter, the maximum explosive force will, generally speaking, be developed at the hollowed portion of theV charge, and the radial forces emanating from this portion of the charge are probably of correspondingly increased magnitude. Accordingly, by positioning the explosive charge so that its base or hollowed end portion is outside the outer end of socket 17, the radial forces from this portion of the charge will be caused to discharge into the relatively large unconned space formed by mouth section 18 and will rapidly dissipate therein without damage to the adjacent portions of the gun body. The outward taper of wall 20 also aids in obtaining this result. An annular clearance of about 1A; inch or more between the exterior of the explosive body at its greatest diameter and the wall of socket 17 will ordinarily be sulicient for elfectively protecting the parts of the gun body from the lateral forces generated by explosion of' the perforating charge. The outer end of the explosive may be positioned at a distance of one-sixteenth inch or more outside the outer end of the socket. In the case knotted end 43 of fuse Cord` of a perforating unit of the form illustrated in the drawings, this spacing will apply to the inner'end of cylindrical' portion 24. The fact that container 28 and sleeve 31 are interposed in the space between the explosive and the wall of socket 17 will not affect theadvantageous results flowing from the provision of the clearance space so long as the materials comprising these elements are appreciably softer or less dense than the steel from whichgun body 10 is constructed.

This invention overcomes the objections of' the previous gun perforators in the following respect: Where such a gun perforator has the hollow detonating charges arranged transversely in a hollow pipe, then upon detonation of'the charges the waves of detonation from one charge will be transm'ittedto the nextcharge so as to displace the same, because the velocity of detonation isgreater than the detonating velocity in the detonating cord;V In accordance with this invention, therefore, means are provided for restricting the transmission of the detonating waves from charge to charge along the carrier. This is accomplished by providing solid material between the charges, which can be conveniently accomplished by making the carrier solid rather than in the form of a pipe, and by providing sockets in the carrier for the detonating charges. This construction, moreover, prevents damage to the carrier itself, which it is desired to retain in order that it may be recharged.

Furthermore, in accordance with this invention, damage to the carrier, incident upon detonation of a charge, is prevented by providing a chamber in the carrier adjacent and surrounding the charge, as shown particularly in Figure 2. If the charge were set directly into a socket, then upon detonation of the charge the socket would be damaged so as to prevent replacement of another charge, except by remachining; in most cases the damage will be such that the carrier could not be used at all. However, the spacing around the charge preserves the carrier itself so that after the carrier has been employed, another charge or set of charges can be inserted.

It will also be noted that the detonating charge is arranged in the carrierk with a seat for the charge projecting the major part of the charge outwardly beyond the seat, as also shown in Figure 2. This prevents damage to the seat upon detonation of the charge. If the charge were set wholly within the carrier, then upon detonation of the charge, the seat would be so damaged as to render the carrier unusable for replacement of other charges.

As shown in Figure 2, the carrier is provided with an outwardly flaring opening 20 at the outer end of the charge. If this ilare were not provided, then upon detonation of the charge, thel stray gases projecting directly against the casing in a well would damage and even split the pipe. However, by the flared construction, the gases are sufciently dissipated to avoid such damage. The

flare is, however, made suiciently sharp so that there will not be a continuous impact of these stray gases against the pipe from charge to charge. In practice the angle to the horizontal Figure 2 is made about 15.

Guns constructed in accordance with the present invention may be made in any desired size and length and with any suitable shot spacing, and may be made in the form of units adapted for end-to-end connection. One suitable gun unit may be about iive feet long having charge sockets spirally oriented along the body on four inch axial spacing, thus providing a total of fifteen shots distributed over the ve foot length of the unit. A plurality of similar gun units may be connected end-to-end to provide guns of greater length, as may be required.

Fig. 6 shows a second gun unit 10a which may besubstantially' identical in construction to the unit previously described, connected to the bottom of thelatter by screwing pin 1S into the box 14a of the lower unit.' The latter is'provide'd'with the same cord-type fuse 39'havingits upperendknotted at 48a, so that when the'units are' lil screwed together knot 48 in the upper unit will be in pressure'fcontact with knot 48av and compressed against the latterffby` the-thrust of pin 15. When detonationfofv the fuse' cord isinitiated at the upper end of such -a l gun string, the'detonation wave will travel from one unit to th`e"nextsettingV off the'perforating charges in all of the units. By this simpleexpedient, a large number of gun units may be connected togetherm and tired simultaneouslyv Gaskets 50 are provided between the as a single gun. various sections;

By placing-knots48 and 4Sain contact in the manner described, the knots lfunction as a booster for the detona-V section thus maintaining high order detonation through-v out the entire string of perforating units and assuring high order. detonation of all of the charges connected to thecord throughout the entire string.

By-the employment-of closure elements 13 constructed as described, it willbe seen that the sealing pressure of liange 351'upon shoulder 19will increase as the pressure applied `to the exterior of the closure element is increased. Accordingly, cap screws 36-36 need be tightened down only suiciently to prevent leakage of uid into sockets 17A at the relatively lowy pressures at the top of the well, andthattheseal will automatically become tighter as the gun yis'vlowered into regions of increasing hydrostatic pressurein kthe welltbore. A relatively simple and cheaply constructed sealing arrangement is thus provided which is effective under any pressures likely to be encountered in wells in which the gun is used.'

A practicaldimensioned embodiment of this invention isiasffollows:

Fig.` 2 is an actual drawing to scale of a perforating gun.

in which thecarrier has an outside diameter of 3.75 inches. The. detonating cord39 is a standard Prima Cord. The explosive container 28 is of high temperature thermosettinggplasticloaded with a charge of 17 grams of Cyclonite:to a:density of 1.53 grams through the mainbody of the charge. thickness of about .035 inch, with a diameter of 1.25 inches, with an interior angle of 90 andwith .25 inch radiusV in the apex. The stand-ott part of cap 32 is of the rupturablealuminum alloy capable of withstanding high pressures and yet shatterable. The distance from the inside of the cap at its center to the base of the liner 27 is 6.25 inch. The distance from the front of the4 seat 19 to the base of the liner at 34, Fig. 2, is .5625 inch. An actualv test of such azwell Yperforating gun with a charge described as. above,v resulted in perforating through'one string of' a 5.5 inch diameter 20 pounds per ft. weight casing and through over l0 inches of cement.

It will be understood the various modifications and alterations may be made in the details of the illustrative embodiment within the scope of the appended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is: l. A perforating gun comprising, a plurality of elongated gun body units adapted to be connected together in end-to-end relation, each unit carrying one or more explosive charges, a separate length of a cord-type detonatingA fuse extendingl longitudinally through each of said gun units in detonating relation to the charges carried thereby, andmeans for transmitting the detonating wave from .the fuse in one of said gun units to the fuse in the next gun unit, saidmeans comprising knots formed in the adjacent ends of said fuses and arranged in the adjacent ends of their respective gun units for axial compression when said units are connected together.

2.V A well perforating gun, comprising, a sectional carrier'desig'ned for placement inside of the well and em- The liner. 27 is of pure copper having a.

bodying a series of coupled sections, a hollow detonatable chemical charge on each section, a single length of a cordtype detonating fuse arranged along each section and con nected to the charge thereon and mutually contacting knots upon the fuses of adjacent sections compressively engaged when the sections are connected together.

3. A well perforating gun, comprising, a sectional carrier designed for placement inside of a Well and embodying a series of coupled sections, each section having a series of longitudinally spaced seats and a series of hollow detonatable chemical charges supportable in said seats, holder means on said seats for supporting the hollowed ends of said charges outwardly beyond said seats, a single length of a cord-type detonating fuze extending longitudinally through each section in detonating relation to the charges seated therein, and means for transmitting the detonating wave from the fuze in one of the sections to the fuze in the next section, said means comprising knots formed in the adjacent ends of said fuzes and arranged in the adjacent ends of their respective sections for axial compression when said units are connected together.

4. In a multi-unit perforating gun, a gun unit, comprising, a tubular body, connection means on the ends of the body for connecting it in end-to-end relation with similar References Cited in the file of this patent UNTTED STATES PATENTS 2,139,104 `JVellS Dec. 6, 1938 2,216,144 Turechek Oct. 1, 1940 2,399,211 Davis et al. Apr. 30, 1946 2,402,153 Elliott June 18, 1946 2,494,256 Muskat et al. Jan. l0, 1950 2,562,880 Andrew Aug. 7, 1951 OTHER REFERENCES Article entitled Casing Perforating With Shaped EX- plosive Charges, by R. H. McLemore, published in The Oil and Gas Journal, issue of December 28, 1946, 4 pages. Copy in Division 70. 

